Perovskite surface treatment with additives has been reported to improve charge extraction, stability, and/or surface passivation. In this study, treatment of a 3D perovskite ((FAPbI 3 ) 1−x (MAPbBr 3 ) x ) layer with a thienothiophene-based organic cation (TTMAI), synthesized in this work, is investigated. Detailed analyses reveal that a 2D (n = 1) or quasi-2D layer does not form on the PbI 2rich surface 3D perovskite. TTMAI-treated 3D perovskite solar cells (PSCs) fabricated in this study show improved fill factors, providing an increase in their power conversion efficiencies (PCEs) from 17% to over 20%. It is demonstrated that the enhancement is due to better hole extraction by drift-diffusion simulations. Furthermore, thanks to the hydrophobic nature of the TTMAI, PSC maintains 82% of its initial PCE under 15% humidity for over 380 h (the reference retains 38%). Additionally, semitransparent cells are demonstrated reaching 17.9% PCE with treated 3D perovskite, which is one of the highest reported efficiencies for double cationic 3D perovskites. Moreover, the semitransparent 3D PSC (TTMAI-treated) maintains 87% of its initial efficiency for six weeks (>1000 h) when kept in the dark at room temperature. These results clearly show that this study fills a critical void in perovskite research where highly efficient and stable semitransparent perovskite solar cells are scarce.

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coefficient and carrier mobilities, and long minority carrier lifetimes. [1][2][3][4][5] Vast amount of research has been conducted on further improving stability and increasing the efficiency of perovskite solar cells. One way of boosting the efficiency of perovskite solar cells is maximizing the photocurrent generation by light management. Light management in perovskite solar cells can be provided by surface texturing, [6][7][8][9][10][11][12][13] plasmonics, [14][15][16] antireflective films on the glass substrate, [17,18] vertical cavity design, [19][20][21][22][23][24][25][26] and photon recycling. [27,28] Among them, vertical cavity design is popular since it does not require any additional material other than what is needed to fabricate a perovskite solar cell, guaranteeing its low-cost.Ball et al. reported optical simulation of glass/fluorine-doped tin oxide (FTO)/TiO 2 /CH 3 NH 3 PbI 3 (MAPI)/Spiro-OMeTAD/Au solar cell structure based on transfer matrix method (TMM), where they reported local maxima in the modeled short circuit current at MAPI thicknesses of ≈190, ≈320, ≈470, and ≈630 nm thanks to favorable interference conditions. [21] However, they did not extend their simulations to cover transport materials (TLs) with different refractive indices. In a recent study, Grant et al. published a comprehensive optical simulation study on MAPI/silicon tandem solar cells using the finite element method. [25] They divided the ideal refractive index of a front transport layer (FTL) of the perovskite top solar cell into two regions: those larger and smaller than the refractive index of MAPI at 1000 nm of wavelength. However, this separation is incapable of explaining single junction perovskite solar cells targeting shorter wavelengths. Filipic et al. provided vertical cavity designs for 2-and 4-terminal (2T and 4T)-MAPI/ silicon tandem solar cells in which, MAPI solar cell is composed of glass, front indium tin oxide (ITO), Spiro-OMeTAD, CH 3 NH 3 PbI 3 , TiO 2 , and rear ITO layers. [23] It is important to note that optimum thickness of a transport layer changes based on 2T and 4T configurations since in 2T configuration nonoptimum layer thicknesses can lead to a photocurrent reduction in the perovskite top cell and its increase in the silicon bottom cell. Therefore, an optical cavity design of a perovskite solar cell resembles that of perovskite top cell in a 4T tandem cell geometry, yet, the effect of replacing the rear solar cell with a planar metal is optically substantial. Although an FTL refractive index (n FTL ) around that of perovskite is commonly suggested in the literature, [20,25] there is no Organometallic halide perovskite solar cells have emerged as a versatile photovoltaic technology with soaring efficiencies. Planar configuration, in particular, has been a structure of choice thanks to its lower temperature processing, compatibility with tandem solar cells, and potential in commercialization. Despite all the breakthroughs in the field, the optical mechanisms leading to highly efficient perovsk...

Photovoltaics with monolithically connected tandem architectures have the potential to achieve high efficiencies owing to enhanced spectral absorption and reduced thermal losses. To achieve this, photoactive layers with complementary absorption and interconnecting layers, which are robust, transparent, and energetically suitable, are essential. Here, we investigate a strategy to create an efficient, highly transparent, ohmic, and chemically robust interconnecting layer based on atomic layer-deposited tin oxide (SnO2) and solution-processed diluted poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), eliminating the need of widely reported parasitically absorbing metal recombination layers. Monolithic perovskite/organic tandem devices built on a metal-free interface (SnO2/PEDOT:PSS) compared to its counterpart (SnO2/metal/PEDOT:PSS) show no significant difference in PCE, but a remarkable enhancement in photostability. Furthermore, tandem solar cells were tested under outdoor conditions for 2 weeks, showing improved stability and solar power conversion than single-junction perovskite and organic devices, underscoring the potential of monolithic tandem solar cells.